This means that you are asking Q++Studio to use the value of nResult as the date to use in some resulting action, but you seem to have forgotten to calculate the value of nResult.

Technically, this is not an error, as the value 0 is an allowable date. But since the date corresponding to the value 0 is December 30th 1899, Q++Studio warns you that this might not be the date you really want to use.